ILIAS Developers: manipulating html of page content

yes you could do something like that in your getHTML() method and in hook.js you then prepend  on the div:

global $DIC;

if ($a_comp == 'Services/Container' && (int)$_GET['ref_id'] === 1234) {
    $DIC->globalScreen()->layout()->meta()->addJs('./Customizing/global/plugins/Services/UIComponent/UserInterfaceHook/.../js/hook.js');
}

it is not ideal as this can influence the user experience.